To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
In general, a signal processing procedure for wireless communication includes channel coding, modulation, frequency up-conversion, and transmission in a transmitting side. In accordance therewith, signal processing in a receiving side includes frequency down-conversion, demodulation, and channel decoding. Herein, the demodulation in the receiving side includes a procedure of calculating a per-bit or per-symbol decoding metric.
To generate the decoding metric, it is necessary to premise a specific probability distribution for an interference and noise signal. The conventional technique assumes a Gaussian distribution for an interference signal to perform decoding with a low complexity. Therefore, a quadrature amplitude modulation (QAM)-series modulation scheme is primarily used in order for the interference signal to be similar to a Gaussian signal to the maximum extent possible.
However, it is generally known that a channel which assumes a non-Gaussian distribution has a greater channel capacity than a channel which assumes the Gaussian distribution. Therefore, if decoding is performed properly, the channel which assumes the non-Gaussian distribution can have a higher decoding performance in comparison with the channel which has the Gaussian distribution.
Accordingly, there is a need to develop a modulation scheme which allows an interference signal to be similar to the non-Gaussian distribution to the maximum extent possible, and as a result, a frequency-QAM (FQAM) scheme is proposed. The FQAM method is a hybrid modulation scheme in which the QAM scheme is combined with a frequency shift keying (FSK) scheme, and has advantages of the QAM scheme having a high spectral efficiency and the FSK scheme allowing an interference signal to have a non-Gaussian distribution.
However, since the FQAM is a new technique proposed recently, a channel quality information feedback scheme different from the conventional scheme is required. A method has been conventionally used in which a signal to interference plus noise ratio (SINR) value is calculated on the basis of channel estimation using a pilot, the calculated SINR value is transmitted by quantizing it through a determined scheme, a modulation and coding scheme (MCS) level is determined on the basis of the calculated SINR value, and an MCS index corresponding to the determined MCS level is transmitted. That is, in a channel quality information feedback of a wireless communication system using the conventional QAM scheme, channel information other than the SINR value has not been used to determine the MCS level.
Since a non-Gaussian distribution for an interference signal is assumed in the wireless communication system using the FQAM scheme, it is difficult to determine an accurate MCS level when only the SINR is simply used, which causes a performance deterioration.